Estrogen and other hormones are known to interact with both normal and malignant cells through specific receptor mechanisms and to effect changes in cell growth, division, and metabolism. The specific changes in cell cycle parameters, as well as the interaction of these hormones with radiation and cytotoxic drugs, are unknown. In this proposal we outline methods of examining the effects of estrogen and other hormones on viability as a function of cell cycle position, as well as the interaction of hormones and radiation and hormones and cytotoxic drugs on an in vitro human breast carcinoma line. To determine the in vitro kinetic parameters we will employ examination of growth curves and % labeled mitosis curves. Clonogenic survival curves and exponentially growing and plateau phase cultures will be employed to ascertain the effect of hormone, x-ray, and hormone, drug, and x-ray interactions in this cell line.